I may be wrong but I am not aware of radios without a power transformer and with a magic eye tube.

They do exist but are a bit uncommon. During the peak of the "magic eye" craze of 1937-38 every two-bit radio sold seemingly had a magic eye; except for the holdouts (Philco and a few others) who were opposed to using RCA-invented eye technology for business reasons. Which in the unlikely event that your ersatz "eye" finds its way into such a radio, it will be necessary to add a resistor to mimic the voltage drop of the actual string-heater-connected tube.

As realized, your "eye" doesn't seem that it would function very effectively as a tuning indicator- not enough resolution from one LED segment to another. Unless I am misunderstanding its implementation- I am assuming that it responds more or less linearly to AVC variations. It might be more useful if it could be made to function as a peak (or, actually, a minimum-voltage) detector offering a nonlinear display response to AVC. That would overcome some of the resolution limitations of using a relatively small number of discrete LEDs but might also reduce some of the "eye candy" appeal of the display (which was probably 90% of the reason these things were present in the first place).

I have seen these in person close up. Except for the glass envelope being in a collar it is very difficult to differentiate the reproduction from the original by appearance or function. They are a bit pricey but there is no phosphor to wear out.

Norman

_________________"No home is complete without music" - Capehart Sound Amplifying and Distributing Systems

I may be wrong but I am not aware of radios without a power transformer and with a magic eye tube.

They do exist but are a bit uncommon. During the peak of the "magic eye" craze of 1937-38 every two-bit radio sold seemingly had a magic eye; except for the holdouts (Philco and a few others) who were opposed to using RCA-invented eye technology for business reasons. Which in the unlikely event that your ersatz "eye" finds its way into such a radio, it will be necessary to add a resistor to mimic the voltage drop of the actual string-heater-connected tube.

As realized, your "eye" doesn't seem that it would function very effectively as a tuning indicator- not enough resolution from one LED segment to another. Unless I am misunderstanding its implementation- I am assuming that it responds more or less linearly to AVC variations. It might be more useful if it could be made to function as a peak (or, actually, a minimum-voltage) detector offering a nonlinear display response to AVC. That would overcome some of the resolution limitations of using a relatively small number of discrete LEDs but might also reduce some of the "eye candy" appeal of the display (which was probably 90% of the reason these things were present in the first place).

Thanks for the information, I am an old EE but fairly new to Radios restoration. As far as my circuit, the LEDs response is linear to the AVC voltage and the LEDs response looks perfectly smooth and without any gaps. Originally I had the same concerns but I was very surprise how good it looked. The AVC voltage change is very quick when tuning a radio so having more LEDs with higher resolution would have NOT make any difference. Take a look at the AVC voltage with an analog voltmeter and you will see what I mean.

I have seen these in person close up. Except for the glass envelope being in a collar it is very difficult to differentiate the reproduction from the original by appearance or function. They are a bit pricey but there is no phosphor to wear out.

Norman

These are stated to be electromechanical devices. I'm guessing it is some sort of rotary movement that drives a mask to expose/obscure the light from a green LED behind the mask.

So, the display is more like that of a shadowmeter than an actual magic eye tube. It really isn't a convincing substitute for an eye tube (especially the EM34, which is a dual-display unit) but does appear to be functional, somewhat original-appearing (at first glance)... and as the page owner comments, better than an empty black hole where a display tube should be.

Is it worth $85 Euros plus shipping? To my way of thinking, not as long as NOS 6E5s are still available from Japan for $20-30 a pop; or 6E5Cs from the former Soviet Union for about the same money. (The latter are good subs for the EM34 if one can tolerate the loss of a dual display). Of course, some day these will all be gone and solid-state substitutes may be the only game in town. Unless some Asian entrepreneur starts manufacturing new hollow-state eye tubes...

It really isn't a convincing substitute for an eye tube (especially the EM34, which is a dual-display unit) but does appear to be functional, somewhat original-appearing (at first glance)... and as the page owner comments, better than an empty black hole where a display tube should be.

Is it worth $85 Euros plus shipping? To my way of thinking, not as long as NOS 6E5s are still available from Japan for $20-30 a pop; or 6E5Cs from the former Soviet Union for about the same money. (The latter are good subs for the EM34 if one can tolerate the loss of a dual display).

I agree about the economics but you should see one in person before passing judgement about whether or not it is a convincing substitute. I have seen them in person and was very impressed with how much they look and operate like an original eye tube. The price may be lower here if the European VAT is included in the posted price (VAT not charged for exports).

Norman

_________________"No home is complete without music" - Capehart Sound Amplifying and Distributing Systems

I agree about the economics but you should see one in person before passing judgement about whether or not it is a convincing substitute. I have seen them in person and was very impressed with how much they look and operate like an original eye tube. The price may be lower here if the European VAT is included in the posted price (VAT not charged for exports).

Norman

So the webpage animation which shows the response of the "tube" is not an accurate depiction of it in operation? It appears to be a simple sweep display which doesn't closely emulate that of the actual vacuum tube... hence my "shadowmeter" comment. Nice green color, though.

Maybe I am being overly critical... no doubt there would be many who would find this device desirable for their radios, even if its operation is not what I would call "authentic". These eye tubes are (and always were) more for looks than function, anyway. Still, I regret having to replace EM34/35-equipped sets with rewired sockets to accept 6E5C tubes- because the 6E5C display looks nothing like that of the EM34.

So the webpage animation which shows the response of the "tube" is not an accurate depiction of it in operation?

The web page depiction does not do the reproduction much justice. There is a difference in operation of the reproductions on the web page in that only one side of the opening is dynamic rather than both.

Norman

_________________"No home is complete without music" - Capehart Sound Amplifying and Distributing Systems

Very nicely done upsss. Good to see a solution using readily available components.

I made an LED 6U5/6E5 replacement a couple of years ago, but I didn't think I'd be able to make a small enough display using discrete LED's. So, I used a multiplexed circular LED display that I found on Ebay which happened to be the right size. The multiplexing made the drive circuitry a lot more complicated though.

Is over-voltage protection needed on the AVC line? Wild things happen in tube circuits especially as they warm up. Most opamps are not rated for input voltages that exceed power rails. From TL082 datasheet, "The magnitude of the input voltage must never exceed the magnitude of the supply voltage or 15 V, whichever is less." Your rails are 8.5v I guess.

Perhaps a series resistor in the AVC line input of your circuit followed by diodes to the rails or 8v zeners, or whatever. The TL082 input won't notice a series resistor below a meg.

Is over-voltage protection needed on the AVC line? Wild things happen in tube circuits especially as they warm up. Most opamps are not rated for input voltages that exceed power rails. From TL082 datasheet, "The magnitude of the input voltage must never exceed the magnitude of the supply voltage or 15 V, whichever is less." Your rails are 8.5v I guess.

Perhaps a series resistor in the AVC line input of your circuit followed by diodes to the rails or 8v zeners, or whatever. The TL082 input won't notice a series resistor below a meg.

This could be a major issue during operation, as sets with the 6G5/6U5 eye tubes close the eye fully at -22 volts on the AVC line but are often capable of delivering much more negative voltage than that on very strong local stations. Any solid state replacement would need to be able to tolerate at least -50 volts to be safe, or a zener clamp would need to be added after an isolating resistor.

_________________Dennis

Experience is what you gain when the results aren't what you were expecting.

That's awesome! I think you'd be able to sell some kits. I'd buy one, even if it's the same price as a "real" eye tube. For me, the issue isn't so much having the radio being authentic when it get's most of it's air time, but rather the idea that I could get some use out of it without using up an eye tube.

I've got a Zenith 7S260 that gets a lot of air time. I obviously want to keep a couple of eye tubes on hand to use it "originally" from time to time, but I love the idea of having some modern replacements for 99% of the time when I just want to listen to some music through a 1930's radio. Keeping some wear and tear off of a short lived eye tube would be great.

As far as protecting the OP-AMP input, it is a good idea (I should have known better), even if you are not expecting your AVC voltage to be any higher than -8V. My receiver with a strong station (practically in a line of sight) the highest AVC voltage measured was less than -6V. The easiest way to protect the OP-AMP input is to clamp the AVC input to the +/- power supply with two small switching diodes (1N4148) and an inline series resistor (~1Meg) to limit the current.

I tried to diffuse the LED light and nothing I tried looked really good, it all made it look very grainy. I ended up lightly sanding the shiny finish of the top of the LEDs which diffused the light through the entire LED body and it ended up looking the best (that is what you see in the video). If I don't end up using any other diffuser, I will probably lower the LEDs current, I think they are too bright.

BTW, if anyone is planing to use this circuit on a radio without a power transformer and with 6.3V filament voltage where one of lines is NOT grounded, you will have to use a small 6v transformer to power just this circuit.

LED's were and maybe still are made with silica optical dispersant within the plastic body. The entire plastic blob glows rather than a hot spot.

Option is to have a few of the LEDs on constantly as they would be in a conventional tube. The "hand" made target gives the option of color bands. No rule it has to be green. Can be red, to orange to green

Sorry, hate to nit pick.

I did look for a flat bottomed plastic or glass tube as an enclosure. Nothing turned up as yet. Salvage of a dead tube may not be practical, once the envelope is cut near the base looses all strength. Some installation have rather crude as well as tight clamps. I can see re-use of the tube base as practical.

I tried to diffuse the LED light and nothing I tried looked really good, it all made it look very grainy.

Michael's Crafts sells a translucent sheet of burnishing plastic that is at least 1500-2000 grit. I found that it makes an excellent projection screen. In your application, the amount of diffusion could be varied by fractions of millimeters from the top of the LED surface.

I wonder what the effect would be if you potted the LED assembly in clear epoxy. Also there may be an admixture to epoxy that would give it a ground glass appearance.

On an LED clock project years ago I needed a diffuser. I sand blasted some glass on the back side next to the LED and it looked nice. Could also use acrylic clear plastic which would be easier to cut or shape. I have sand blasted logos and patterns into that and then use LEDs along the edge light up the logo. Edge lighting of sandblasted acrylic produces a very soft almost fuzzy light.

Perhaps you could eventually offer a kit and include the necessary protection components for the op-amp and the correct base depending on the tube type with the circuit optimized for the tube it is replacing.

There's another neat (non-electromechanical) solution which looks closer to the original tube display than LED's. It uses a PIC driven small color LCD display array and is MUCH more than a simple "magic eye": it is fully programmable (6 different background colors, including the standard green) and can also display numerical relative signal strength in %, B+ voltage, frequency (with programmable IF offset),etc... of course these numerical displays can be disabled if you want to maintain the original "green eye" look. The module is compatible with most magic eye tubes (EM34, EM4, 6AF7,...) and doesn't require an additional external power supply or transformer. The (fully assembled) module is very affordable for what it does at 35€ (about 43$)I have no affiliations with this seller other than as a satisfied customer who bought it and can confirm it works as intended.